Etching apparatus and methods

Abstract

A method is for etching the whole width of a substrate to expose buried features. The method includes etching a face of a substrate across its width to achieve substantially uniform removal of material; illuminating the etched face during the etch process; applying edge detection techniques to light reflected or scattered from the face to detect the appearances of buried features; and modifying the etch in response to the detection of the buried feature. An etching apparatus for etching substrate across its width to expose buried is also disclosed.

What is claimed is: 
     
       1. Etching apparatus for performing an etch operation of globally etching a substrate across its width to expose buried features, including: (a) an etch chamber; (b) a support fixed in place within the etch chamber and dedicated to retain the substrate in the etch chamber, the support having a support surface oriented horizontally such that when the substrate is generally planar and is retained by the support, a face of the substrate to be etched is oriented horizontally generally parallel to the support surface; (c) an illumination source having an optical axis and which emits light propagating in the direction of the optical axis, the illumination source being mounted in the apparatus as oriented relative to the support such that the optical axis of the illumination source extends at an acute angle with respect to the support surface and light emitted by the illumination source will illuminate the face of the substrate, retained by the support on the support surface, at an acute angle with respect to the face; (d) a camera positioned relative to the support to capture light reflected or scattered from the face at an acute angle with respect to the support surface; (e) an edge detector coupled to the camera and configured to detect the appearance of an edge of at least the buried features emerging on the face during the etch operation, and (f) a controller operatively connected to the edge detector and configured to stop the etch operation in response to the appearance of the at least one edge of the buried feature when detected by the edge detector. 
     
     
       2. Apparatus as claimed in  claim 1 , wherein the edge detector includes a Sobel filter. 
     
     
       3. Apparatus as claimed in  claim 1 , wherein the etch chamber has opposed walls and windows in the opposed walls, respectively. 
     
     
       4. Apparatus as claimed in  claim 3 , wherein the illumination source comprises a light source external to the etch chamber and positioned to generate light that passes through one of the windows. 
     
     
       5. Apparatus as claimed in  claim 3 , wherein the camera is external to the etch chamber and positioned to receive the reflected or scattered light through one of the windows. 
     
     
       6. Apparatus as claimed in  claim 1 , wherein the controller comprises a comparator. 
     
     
       7. Apparatus as claimed in  claim 1 , wherein the controller comprises a delay. 
     
     
       8. Apparatus as claimed in  claim 1 , wherein the illumination source and the camera are external to the etch chamber. 
     
     
       9. Apparatus as claimed in  claim 8 , wherein the illumination source and the camera are fixed in place in the apparatus relative to the etch chamber. 
     
     
       10. Apparatus as claimed in  claim 1 , wherein the edge detector is configured to detect the appearance of an edge of a surface having a diameter of 10 μm in or less. 
     
     
       11. Apparatus as claimed in  claim 10 , wherein the edge detector includes a Sobel filter. 
     
     
       12. Apparatus as claimed in  claim 10 , wherein the camera has pixels that are of a size too large to capture an image of a surface smaller than 10 μm in diameter.